Implement Phase 1 backend: FastAPI upload API with MinIO and PostgreSQL

- Add FastAPI app with CORS and auth middleware (Bearer token)
- Add POST /api/v1/transactions/upload endpoint (multipart/form-data)
- Add MinIO storage service with date-partitioned object keys
- Add PostgreSQL database service for transaction metadata
- Add Dockerfile and docker-compose.yml for deployment
- Add config.example.yaml template

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/main.py

@@ -0,0 +1,20 @@
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+from app.auth import AuthMiddleware
+from app.routers import upload
+
+app = FastAPI(
+    title="SnapLedger API",
+    version="0.1.0",
+)
+
+app.add_middleware(AuthMiddleware)
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+app.include_router(upload.router, prefix="/api/v1")